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  1. #1
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    Caliper piston seals?

    Car brakes have them. Motorcycle brakes have them. Caliper pistons sticking is relatively rare as long as the seals are intact.

    Unless I'm missing something inherently different about bicycle brakes, it seems as though a considerable percentage of 'issues' with hydros is water contamination of fluid and piston sticking and its consequences. Even with oil brakes there is nothing to keep the dirt out.

    I can live with routine futzing with my caliper pistons to keep them free and even, but doesn't anyone think it passing strange that they sell brake bleed kits to the public when most motorcycles and cars out there have never had their brakes bled - ever?

    I realize that each brake would have to have two rubber sealing boots and four grooves to machine, but considering that stopping reliably is - next to having your wheels fall off - top of the list for safety would the cost be that significant?

    Please sir, may we have some seals?

  2. #2
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    They would be tiny and oh so cute!
    BTW: Cars and motos do bleed their brakes.

  3. #3
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    Quote Originally Posted by the-one1 View Post
    They would be tiny and oh so cute!
    BTW: Cars and motos do bleed their brakes.
    Cute has nothing to do with it. And they would be about 20 some mm in diameter. And how long would a car brake go without a seal? About six weeks in winter, maybe.

    I'm a car and motorcycle mechanic so I've been through a lot of brake work over time. I'm just saying you can buy a $4000 motorcycle with disc brakes that are hydraulically maintenance free for ages whereas a $4000 bicycle has unsealed hydraulics like a '30s English car.

    I just think it's a shame on the industry that this sort of lameness happens. Unless someone can give me a good reason why. So far no takers.

    Having to extend the pistons out and clean them and lube with brake fluid is pretty retarded IMO.

  4. #4
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    Quote Originally Posted by bulerias View Post
    Having to extend the pistons out and clean them and lube with brake fluid is pretty retarded IMO.
    Yup.

    I'm not a fluid engineer, but I think it has to do with the fact that MTBs can't seem to seem to handle a closed system. On a mountain bike, the entire system has a much, much smaller volume of fluid in a much smaller system, so as the fluid heats up, its FAR more sensitive to expansion than on a larger system with more volume (i.e., motorized vehicles). When you're already working with tiny pad clearances, even a minimal degree of expansion in a closed system could render the brakes inoperable. In a car, however, the system is larger and is capable of accommodating the thermal expansion that the fluid endures.

    Companies have tried. Brembo, for example, made a closed MTB brake . . . . and now Brake Force One. There's a reason that the Brembo's aren't around anymore . . . and don't say its because Brembo doesn't know brakes.

    Edit: NM . . . this is completely irrelevant to your question. Carry on.
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  5. #5
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    Quote Originally Posted by bulerias View Post
    Car brakes have them. Motorcycle brakes have them. Caliper pistons sticking is relatively rare as long as the seals are intact.

    Unless I'm missing something inherently different about bicycle brakes, it seems as though a considerable percentage of 'issues' with hydros is water contamination of fluid and piston sticking and its consequences. Even with oil brakes there is nothing to keep the dirt out.

    I can live with routine futzing with my caliper pistons to keep them free and even, but doesn't anyone think it passing strange that they sell brake bleed kits to the public when most motorcycles and cars out there have never had their brakes bled - ever?

    I realize that each brake would have to have two rubber sealing boots and four grooves to machine, but considering that stopping reliably is - next to having your wheels fall off - top of the list for safety would the cost be that significant?

    Please sir, may we have some seals?
    I agree

    It would seem fairly easy to put a seal boot in a caliper...it could even help retact the pads.

  6. #6
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    I think this has already been discussed and one of the main point was that MTB calipers wouldn't be able to put up with the added stiction of have piston seals, since they are way smaller than a car or motorcycle system.

    But otherwise I don't know.
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  7. #7
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    It isn't really a seal that is being discussed but a flexible boot over the end to keep the water and dirt out. It's a seal but not of the sliding but folding type. Resultant friction should be less.

    A lip seal would be another possibility but that's not what I've seen on other brakes.

  8. #8
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    It's really just a dust cap but that little rubber bellows keeps a lot of crud away from the piston O-ring.

    I think demand for light weight components and manufacturing costs play a significant role as to why these are omitted.

  9. #9
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    Quote Originally Posted by David C View Post
    I think this has already been discussed and one of the main point was that MTB calipers wouldn't be able to put up with the added stiction of have piston seals, since they are way smaller than a car or motorcycle system.

    But otherwise I don't know.
    No added stiction is neccesary.

    The seal is attached to the caliper and to the piston no relative motion...

    The exterior dirt seal flexes....it doesn't slip.

  10. #10
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    Oh, sorry, now I see what you mean. My bad. Perhaps the heat would also be an issue at some point ? Either in the long run and cause reliability issues or can't be durable enough to fit in the already tight clearance a MTB caliper offer ?

    I'm sure we'll see some of it soon enough, when they will need a new feature to boots the sales
    Quote Originally Posted by NicoleB28 View Post
    topless. that's what all mtb girls do. we go ride, get topless, have pillow fights in the woods, scissor, then ride home!

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